1. Field of the Invention
The present invention relates to a rotary electric apparatus, and in particular, to a synchronous machine such as synchronous motor generator.
2. Description of the Related Art
There are a variety of types of rotary electric apparatuses and one type of such apparatuses is called synchronous machines. The synchronous machine is provided with a stator and a rotor, in which AC armature currents flow through the stator so that a rotary magnetic field is produced to rotate the rotor synchronously with the rotary magnetic field. As the rotors of the synchronous machines, there are known a magnet type rotor, a field winding type rotor, a reluctance type rotor, and a rotor in which those types are combined.
In the field winding type of synchronous machines, it is not necessary to mount costly permanent magnets to the rotor core. Thus, it is not necessary to take it into consideration the fact that resistance is generated against the centrifugal force applied to the permanent magnets. Besides those advantages, because the current made to flow through the field windings is able to arbitrarily control torque and voltage to be generated (induced), this field winding type of synchronous machine has a practical use in such applications as speed-variable rotary electric machines for generating power for driving automobiles. Japanese Patent Laid-open Patent Publication No. 7-95790 exemplifies a brush-less, easy-to-control torque synchronous machine of field winding type.
However, in the field winding type of synchronous machine disclosed by the above patent publication, it is necessary to flow multiphase AC currents through windings on the stator. The AC currents are in synchronism with the position of the rotor and are amplitude-modulated with the wave of a modulating signal whose frequency is biased. This current flow will cause larger ripples in the currents flowing through the rotor windings, causing larger ripples in the generated torque (torque ripples).
Another field winding type of synchronous machine is disclosed by Japanese Patent Laid-open Publication No. 11-18337, which is also provided with a structure for generating magnetic fields by supplying a current to a stator coil, without using magnetic fields from magnets. Because field windings are wound in the rotor, it is required for this type of machine to have a structure for securing the field winding to the rotor even if the centrifugal force is applied to the rotator. It is also required to assemble the field windings with the rotor.
To meet those requirements, the synchronous machine disclosed by Japanese Patent Laid-open Publication No. 11-18337 has structures shown in FIGS. 47A and 47B. As shown in FIG. 47A, a rotor 20X is divided into magnetic salient poles 21X and a rotor core 21X and field windings 22X are wound around the magnetic salient poles 211X, respectively, so that assembling work is improved. To prevent the field winding 22X from coming off outward in the radial direction due to the centrifugal force, a fan-shaped flange 211Y is integrally formed at the top of each magnetic salient pole 211X.
However, in the conventional structure of this rotor, there should be, in no small measure, a gap between a contact face 211Z of the magnetic salient pole 211X and a contact face 21Y of the rotor core 21X. This is because the separated members 211X and 21X are combined together when being assembled. The gap becomes magnetic resistance, reducing the magnetic flux passing therebetween, thus reducing an amount of available magnetic flux by the machine.
In addition, both faces 211Z and 21Y are located at the root portion of each magnetic salient pole 211X, which means that a slight gap between both members 211X and 21X gives rise to a large amount of reduction in the magnetic flux, deteriorating the performance of the machine.
The gap is liable to be larger, because both faces 211Z and 21Y are formed into a wedge shape. Adopting the wedge shape intends to prevent the magnetic salient pole 211X from coming off from the rotor core 21X.